1. Field of the Invention
The present invention relates in general to apparatus for docking marine vessels alongside other marine vessels or structures and for transferring personnel or equipment between the vessels and structures, and more particularly, to such apparatus for use on vessels and structures having a variable draft.
2. Description of the Prior Art
In the past, many apparatus and methods have been devised for docking vessels at sea and for transferring personnel and equipment between them. This docking and transfer is particularly a problem where one or both of the vessels has a variable draft or where wave action causes the vessels to move with respect to each other. Incidentally, as used herein, the term "draft" means the level of water with respect to the vessel. Also, the term "vessel" as used herein is defined broadly so as to include marine structures. One problem presented by variable draft is that it prevents a single level stationary platform on one vessel from meeting and engaging a single level stationary platform on the other vessel. This problem led to the development of multiple level platforms or ladders allowing transfer at various levels depending on the present draft condition. This, however, proved to be unsafe since a ladder or platform which is frequently submerged becomes coated with algae and the like and is consequently very slippery. This problem is, of course, accentuated when wave action or wind makes climbing a ladder or standing on a platform difficult even without algae.
Another way of meeting the problem of variable draft is to move a platform or stairway up or down to adjust for the variation in draft. Apparatus to achieve this type of result are shown in U.S. Pat. Nos. 3,841,439 and 4,115,887. In these patents a platform along the side of a vessel is raised and lowered by cables attached to a winch. A first ladder is joined to the side of the platform and extends to the deck to allow persons to move between the deck and the platform. The slope of the first ladder varies with the adjustment of the platform. A second ladder extends down from the platform to the docking ship. In U.S. Pat. No. 4,115,887, a turning weight urges the platform against the ship's side to make the platform more steady during wave action. As indicated by the necessity of the turning weight just described, the devices shown in these patents are subject to undesirable movement since their lower ends may not be attached to the ship. Another disadvantage of these devices is the requirement of an operator for the winches. This operator must be located in such a position that he can see both the platform and the docking vessel during operation of the platform. It is also to be noted that these devices do not have a bumper system to fend the docking vessel from the vessel to which the platform is attached.
In U.S. Pat. No. 3,426,542 a dock and ladder system is shown in which a fendering dock assembly is moved up and down by suspending cables. This allows adjustment for the variable draft created by tides on a marine structure such as an offshore drilling platform. This device also suffers from the requirement of an operator. Furthermore, it is a complicated and expensive device.
Several different fender devices have been developed for use on offshore structures or vessels such as drilling platforms and storage vessels. Usually these fender devices provide a solid fender which is flexibly attached to the vessel. Such fenders are shown in U.S. Pat. Nos. 3,564,858; 3,675,610, and 3,901,040. A disadvantage of each of these fender devices is that they do not provide a safe means for transferring personnel and equipment from the docked boat.
It is accordingly an object of the present invention to provide an improved boarding and fender apparatus for use on variable draft vessels.
It is also an object of the present invention to provide such a boarding and fender apparatus having improved safety features.
Yet another object of the present invention is to provide such a boarding and fender apparatus which is both simple and economical.